1. Field of the Invention
The invention relates to a method for determining the quality of a screw joint tightening process, wherein the screw joint is tightened by means of a torque impulse wrench.
2. Description of the Related Art
There is a problem to correctly determine the status and/or quality of a screw joint tightening process, including the result of the tightening process, when using a torque impulse wrench for tightening the screw joint. Ultrasonic technique, i.e. measuring the time of flight of ultrasonic waves through the screw joint, has been used to get an indication of the clamp load obtained by the screw joint at a completed tightening process. Although the accuracy of this clamp load indication method in most cases is accurate enough it may not be good enough to get that high degree of reliable clamp load indication required at high precision screw joints. In addition, there are a number of cases where the screw joint parts are faulty and unable to result in an acceptable screw joint quality. For example, some screw joints may suffer from a wrong clamp length, premature yield, peak-jumping etc., which influence negatively on the screw joint quality after tightening. These problems are not safely detected by the ultrasonic method alone.
A conceivable way to solve this problem might be to combine the clamp load indication obtained via measurement of the ultrasonic wave flight time through the screw joint by for instance a torque measurement such that two independent readings would reveal any faults of the screw joint or the tightening process. Because of the inherent intermittent dynamic action of an impulse wrench, however, it is impossible or at least very difficult to get reliable information of the delivered torque magnitude by using a torque sensor in an impulse wrench.